The present invention relates to a device to measure the alignment of a laser amplification system. It can be applied especially to power lasers requiring the use of several cascade-connected optical amplifiers in a multiple-passage structure.
To make a power laser, the signal prepared by a low-power laser called a pilot laser is generally amplified by means of optical amplifiers consisting, for example, of neodymium-doped glass plates associated with flash lamps. The requisite power level is obtained by the successive crossing of a large number of these plates. The association of several plates constitutes an elementary amplifier.
To optimize the extraction of the energy stored in these amplifiers, a structure known as a multiple-passage structure is used. This structure enables the beam to cross each elementary amplifier several times.
One of the techniques that may be used to obtain several passages through each amplifier is that of the spatial or angular multiplexing of the beams during the different passages. This technique, for the spatial filtering of the beam during the path between two successive amplifiers, uses the method of focusing the beam on the center of a filtering hole. The focusing points are distinct for all the paths of the system.
One of the difficulties of this technique of multiple-passage amplification is that of centering the beams in the amplifiers and in the filtering holes. The centering must be done for each laser-firing operation for it is impossible, from one firing operation to another, to ensure the stability of the optical system which gets deformed owing to mechanical and thermal constraints.
A step-by-step method cannot be envisaged when a large number of systems has to be used simultaneously as, for example, in the case of thermonuclear fusion which may require the focusing of more than 200 laser beams on a deuterium target with a size of some millimeters to transmit the desired power to this target. An automatic alignment device with high-speed performance characteristics is then needed.